Native quaternary structure of bovine alpha-crystallin

alpha-Crystallin is the most important soluble protein in the eye lens. It is responsible for creating a high refractive index and is known to be a sm all heat-shock protein. We have used static and dynamic light scattering to study its quaternary structure as a function of isolation conditions, temp erature, time, and concentration. We have used tryptophan fluorescence to s tudy the temperature dependence of the tertiary structure and its reversibi lity, Gel filtration, analytical ultracentrifugation, polyacrylamide gel el ectrophoretic analysis, and absorption measurements were used to study the chaperonelike activity of a-crystallin in the presence of destabilized lyso zyme. We have demonstrated that the molecular mass of the in vivo alpha-cry stallin oligomer is about 700 kDa (alpha(native)) while the 550 kDa molecul e (alpha(37 degrees C,diluted)), which is often found in vitro, is a produc t of prolonged storage at 37 degrees C of low concentrated alpha-crystallin solutions. We have proven that the molecular mass of the alpha-crystallin oligomer is concentration dependent at 37 degrees C. We have found strong i ndications that, during chaperoning, the alpha-crystallin oligomer undergoe s a drastic rearrangement of its peptides during the process of complex for mation with destabilized lysozyme. We propose the hypothesis that all these processes are governed by the phenomenon of subunit exchange, which is wel l-known to be strongly temperature-dependent.